1. Field of the Invention
The present invention relates generally to an internal combustion engine of the type wherein coolant is "boiled off" to make use of the latent heat of evaporation of the coolant and the coolant vapor used as a heat transfer medium, and more specifically to an improved temperature control arrangement therefor which can adjust the engine temperature appropriately in response to engine load.
2. Description of the Prior Art
In currently used "water cooled" internal combustion engines, the engine coolant (liquid) is forcefully circulated by a water pump through a circuit including the engine coolant jacket and a radiator (usually fan cooled). However, in this type of system a drawback is encountered in that a large volume of water is required to be circulated between the radiator and the coolant jacket in order to remove the required amount of heat. Further, due to the large mass of water inherently required, the warm-up characteristics of the engine are undesirably sluggish. For example, if the temperature difference between the inlet and discharge ports of the coolant jacket is 4 degrees, the amount of heat which 1 Kg of water may effectively remove from the engine under such conditions is 4 Kcal. Accordingly, in the case of an engine having 1800 cc displacement (by way of example) operated at full throttle, the cooling system is required to remove approximately 4000 Kcal/h. In order to achieve this a flow rate of 167 l/min (viz., 4000 - 60.times.1/4) must be produced by the water pump. This of course undesirably consumes a number of horsepower.
Moreover, with the above type of engine cooling system, the temperature of the coolant is prevented from boiling and maintained within a predetermined narrow temperature range irrespective of the load and/or mode of operation of the engine, despite the fact that it is advantageous from the point of fuel economy to raise the temperature of the engine during low-medium load "urban" cruising and reduce same during high speed and/or high load (full throttle) modes of operation for engine protection.
One arrangement via which the temperature of the engine may be varied in response to load is disclosed in U.S. Pat. No. 2,420,436 issued on May 1947 in the name of Mallory. This document discloses an arrangement wherein the volume of water in the cooling system is increased and decreased in response to engine temperature and load. However, with this arrangement only the water level in the radiator is varied while the water jacket, formed in the cylinder block and cylinder head, remains full under the influence of a water circulation pump. Accordingly, this arrangement has suffered from the drawback that a power consuming water circulation pump is required, the amount by which the temperature can be increased is limited by the fact that the water is prevented from boiling and in that the notable mass of water increases the weight and warm-up time of the engine.
Another arrangement of achieving the desired temperature control has included the use of a "dual" cooling system including two radiators which can be selectively used in response to engine load. However, the weight of such a system is prohibitive while simultaneously incurring the drawbacks of slow warm-up and limited temperature variation range.